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April 12, 1932. w. L.-CASPER .COIL

Filed Npv. 10, 1928 wmwMMm864 INVENTOR W. L. CA SPER 5:;

A r Tom/B Patented Apr. 12, 1932 UNlrEnj-sTATEs PATENT OFFICE WILLIAM L.CASPER, OF SUMMIT, NEW JERSEY, ASSIGNOB TO WESTERN ELECTRIC COMPANY,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK COILApplication filed November 10, 1928. Serial No. 318,380.

This invention relates to electromagnetic devices and more particularlyto repeating coils for telephone systems.

An object of the invention is to increase the v range of current densityover which a transformer is highly effective.

A more particular object is to improve the effectiveness of longtransmission lines which include transformers for transmittingalternating currents.

For example, a certain type of telephone system, which may have itseifectiveness increased by the use of repeating coils in accordance withthe invention, employs for 16 ringing purposes alternating currents ofabout 16% or 20 cycles per second. The

E. M. F. of this .frequency impressed upon a given line is in theneighborhood of 100 volts. The E. M. F. upon the primary terminals of IDthe first repeating coil may be, for example,

in the neighborhood of 80 volts. The 20 cycle current isgreatly'attenuated due to the line resistance, and the E. M. F. acrossthe terminals of a second repeating coil connected to the first by arelatively long line may be, for example, in the neighborhood of 10 or20 volts. A coil which'for a call in one direction may be transmittingwill for a call in the other directi n be receiving. With re peatingcoils as heretofore constructed their effectiveness is relatively'highfor transmitting impressed voltages in a medium range of 20 to volts buttheir effectiveness falls off above and below this range. It thereforeoccurs, in the case of a relatively long line connected to two terminallines by means of repeating coils, that neither of the coils is workedwith a high degree of eflectiveness;

Any means which would increase the effectiveness of such repeating coilsat relatively low applied voltages, or at relatively high appliedvoltages, or at both high and low voltages would improve their operationand the Operation of systems in which they are employed. The benefits ofthe improvement are realized on the longer lines where the need forthemis greatest.

By using in the repeating coil cores two suitably selected magneticmaterials in parallel an improvement may be effected. A

transformer having such a core, when properly designed. will have therange of its effectiveness increased. In particular, the efficiency atlow and high current densities may be improved.

Others have heretofore experimented with magnetic cores composed of twomaterials in parallel but it is not thought that any one has recognizedany utility in such devices for improving the practical arts or thatanybody has proposed to apply two or more materials in cores of coilsfor useful purposes. So far as known, any such prior investigations havehad a purely scientific basis.

The present invention is more particularly disclosed in connection withthe accompanying drawings in which:

Fig. 1 represents, in a diagrammatic manner, a repeating coil havingprimary and secondary windings, the core of the coil consisting ofalternate layers or laminations of silicon steel and high permeabilitynickel-iron alloy commonly known as permalloy, and

Fig. 2 comprises graphs indicating, in a relative manner, theimprovement which may be effected by means of such a coil as shown inFig. 1.

In compiling the data for the graphs of Fig. 2 a 20 cycle current wasimpressed upon the primary winding of each of several repeating coilsand the effective impedances for various E. M. F.s of the current noted.The impedances are plotted in ohmsXlO. It is well-known that theeffectiveness of such a repeating coil for a particular low frequency isreduced substantially proportionally to the reduction in impedance at aparticular value of current.

Curve A indicates the impedance or effectiveness at various appliedvoltages of a commercial type of coil with a core of Norway iron. Itwill be seen that the efiiciency curve is fairly flat and fairly high atto volts but falls off to a low value at 10 to 20 volts. I

Curve B relates to a coil having a silicon steel core. From 10 to 20volts impressed E. M. F. the values are higher than in the case ofnickel-iron but from 55 volts upward the impedance and hence theeffectiveness is heat treated to have high permeability at lowmagnetizing forces.

This coil had increased effectiveness at low voltages but theeffectiveness fell ofi' very rapidly above volts.

Curve E relates to such a coil as is illustrated in Fig. 1. In this casethe core consisted of alternate laminations of silicon steel 1, (seeFig. 1) and of a high permeability nickel-iron alloy 2 of a compositionnot exactly determined but somewhere in the neighborhood of to nickeland the balance iron. It will be seen that there is a peak in theimpedance or effectiveness curve at around 7 volts, also that theimpedance and hence the effectiveness is relatively high and relativelyuniform over a wide range, and that in the voltage range between 60 and85 volts the curve lies above all the others. The improvement depends,in part, at least, upon the fact that the .materials have their maximumpermeabilities in widely different ranges of magnetizing force.

Composite cores of other properly selected materials may also be useful.For example, a combination of Norway iron and high permeabilitynickel-iron alloy has been proposed as well as a combination of siliconsteel and Norway iron.

A recently developed magnetic alloy comprising about 50% iron and 50%cobalt when properly heat treated has a very high permeability in arange of magnetizing forces from 5 to 75 gauss. Another, in carrying thepresent invention into effect, has proposed the use of alternate layersof such a composition with silicon steel or with a nickel-iron alloyheat treated to have very high permeability in a low range ofmagnetizing forces. Those nickel-iron alloys having around 78 nickel arevery suitable for this purpose while'others having between 45% and 85%nickel serve quite well. A combination of cobalt-iron, high permeabilitynickel-iron, and high permeability nickel-ironwith chromium added isalso within the scope of the invention.

The invention is not restricted in its application to repeating coilsbut may be applied usefully to other transformers and otherelectromagnetic devices in which it is desired to increase the range ofE. M. F. or current density for which the devices are highly eifective.For example, it will be obvious from curve E of Fig. 2 that a choke coilhaving a core in accordance with Fig. 1

ing of substantially continuous parallel sections of a nickel-iron alloyof 45 to 85% nickel and silicon steel.

In witness whereof, I hereunto subscribe my name this 8th day ofNovember, 1928.

WILLIAM L. CASPER.

